This is a joint Harvard-Brandeis program project, with goals that include both methodological developments and cell-biological applications. The four major goals are: (1) advance methods for obtaining atomic models of large structure by docking and refining atomic models of the component parts in molecular maps from electron cryomicroscopy (cryoEM); (2) improve the accuracy and resolution of the molecular maps we can obtain from cryoEM of single particles, accelerate 2D crystal structure determination, through development of molecular replacement and phase extension methods; (4) improve use of molecular maps from cryoEM to initiate phase determination in studies of large assemblies. By x-ray crystallography. There are four major projects, three cores, and a set of associated projects. The major and associated projects focus on the following biological systems: (1) the actin cytoskeleton; (2) viruses and viral entry into cells; (3) membrane proteins, especially members of the MIP and MAPEG families; (4) antibiotic peptide synthetases; (5) spliceosome assemblies; (6) the phase T7 replication complex, ("replisome"). The cores, which are a central component of the collaborative effort, support shared state-of-the-art electron microscope facilities, software development, and administration of the consortium.